High power factor ( 0.99) can easily be achieved by active PFCs based on the switch mode power converter topologies operating in either continuous-conduction mode (CCM) or discontinuous-conduction mode (DCM). For CCM correctors, the input current is shaped to be sinusoidal superimposed with high frequency ripples and the power factor could approach unity for small ripple amplitude. However, DCM control usually reduces the circuit complexity which translates to lower production cost and particularly suitable for low power applications. The main drawback is the excessive high frequency harmonics generated by the discontinuous conducting current and the attenuation of these switching ripples is usually required to arrive at a nearly sinusoidal input current for high power factor....[ Read more ]

High power factor (> 0.99) can easily be achieved by active PFCs based on the switch mode power converter topologies operating in either continuous-conduction mode (CCM) or discontinuous-conduction mode (DCM). For CCM correctors, the input current is shaped to be sinusoidal superimposed with high frequency ripples and the power factor could approach unity for small ripple amplitude. However, DCM control usually reduces the circuit complexity which translates to lower production cost and particularly suitable for low power applications. The main drawback is the excessive high frequency harmonics generated by the discontinuous conducting current and the attenuation of these switching ripples is usually required to arrive at a nearly sinusoidal input current for high power factor.

Although DCM control scheme in PFC plays an important role in power processing, power factor analysis mainly concern about the CCM operation and the filtered input current with negligible ripples. In this research, a detail analysis of PFC operating in DCM with the high frequency switching ripples are presented. Three common PFC topologies, the PWM boost, the PWM flyback and the hysteretic boost correctors are investigated. The DCM input current is modeled as a series of triangular pulses and the solutions of the root mean square input current and average input power are formulated based on these models, from which the power factors are derived. The total harmonic distortion of the DCM input currents are computed according to the power spectrums of the three correctors and the relation between the discontinuity of the input current and power factor can be evaluated. Circuit simulations and experimental results are presented to verify the theoretical analysis.